Cap for closing a vial



FIG. 1 is a top front perspective view of a cap for closing a vial showing the claimed design;

FIG. 2 is a bottom front perspective view thereof; and,

FIG. 3 is a front view thereof.

Portions of the cap for closing a vial that are not shown form no part of the claimed design.

The broken lines in the figures show portions of the cap for closing a vial that form no part of the claimed design. 

CLAIM The ornamental design for a cap for closing a vial, as shown and described. 